The use of various bismuth salts as a catalyzing and/or corrosion protection constituent in lead-free CED coating agents is described repeatedly in the patent literature, for example, in U.S. Pat. Nos. 5,936,013, 5,702,581, 5,554,700, 5,908,912, 6,174,422, 5,670,441, WO 96/10057, U.S. Pat. No. 5,972,189, WO 00/50522, U.S. Pat. No. 6,265,079, EP 1 041 125, WO 00/47642, WO 01/51570.
U.S. Pat. No. 4,419,468 discloses CED coating compositions which contain 100 to 2000 ppm of polycarboxylic acids as additives for reducing or preventing discoloration caused by metal ions of the baked coatings deposited from the CED coating compositions.
None of the above-stated literature references discloses the simultaneous use of bismuth compounds and dicarboxylic acids in CED coating compositions.
It has been found that the addition of small quantities of selected dicarboxylic acids to lead-free CED coating compositions containing bismuth compounds has a catalytic action on crosslinking of coating layers deposited therefrom on baking.